1 fluorite like dispersion, 4 super low dispersion
See and Buy this product on Amazon.com store (affiliate):
[Tested on a 42 MP camera] It can deliver sufficient resolution to essentially match the detail captured by Sony’s own 100-400 G Master zoom at a considerably lower price, albeit not quite with the same degree of biting contrast [...] The G Master fights back with an aperture that’s one third of a stop brighter [...], closer focusing especially at 400mm, better stabilisation, more confident focusing [...] Sigma’s 100-400mm deservedly earns a recommendation.
It makes that versatility and performance accessible to the average photographer that doesn’t have deep pockets or who does photography for pleasure rather than profit. Sigma has managed to take what was good about the original 100-400 Contemporary and improve on nearly all its weaknesses, and the end result is a well-rounded third party alternative to the much more expensive G Master lens.